Improvement in telephones



A. E. DOLBEAR. Telephone.

No.199,041. Patented Jan. 8,187 8.

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N PETERS. PHOTO-LIYNDGRAPNER, WASHINGTON o c UNITED STATES PATENTOFFIon;

AMOS EMERSON DOLBEAB, OF SOMERVILLE, MASSACHUSETTS, ASSIGNOR TO THE GOLDAND STOCK TELEGRAPH COMPANY, OF NEW YORK CITY.

IMPROVEMENT IN TELEPHONES.

Specification forming part of Letters Patent No. 199,041, dated January8, 1878; application filed December 6, 1877.

CASE B.

To all whom it may concern Be it known that I, AMos EMERSON DoL- BEAR,of Somerville, in the county of Middlesex and State of Massachusetts,have invented certain new and useful Improvements in TelephonicInstruments, which improvements are fully set forth in the followingspecification, reference being had to the accompanying drawings.

My invention relates to a certain class of instruments technically knownas telephones, which are especially adapted to the transmission andreproduction at a distance of sonorous waves or vibrations of everydescription by means of electrical impulses traversing a circuit ofconductors.

My improvements consist, first, in combinin g, with thepermanently-magnetic cores and elastic diaphragm of a telephonicinstrument, an electro-magnet, attached to and supported by saiddiaphragm, and so arranged as to act as an armature to thefirst-mentioned cores; second, in interposing suitable dampers, composedof india-rubber or other equivalent substance, between the poles of themagnetic cores and the armature thereof, or the elastic diaphragm, inorder to destroy interfering vibrations; and, third, in an improvedalarm attachment for telephonic instruments.

In the accompanying drawings, Figure 1 is a plan view, partly insection, of my improved instrument. Fig. 2 is a vertical transversesection of the same, taken in the plane of the dotted line a; a: in Fig.1, the permanent magnet and its attachments being removed.

The instrinnent shown in the drawings is adapted to be used either as atransmitting or as a receiving instrument, and in its generalconstruction and arrangement is similar to that described in my formerapplication now pending in the Patent Oflice, designated as Case A,which was filed on the 31st day of October, 1877, and to which referenceis had.

My present improvement relates more especially to the construction andarrangement of the elastic diaphragm and inductor.

In Figs. 1 and 2, a is the base of the instrument. b is a permanentmagnet, which may be of the U or horseshoe form, and composed either ofseparate laminae or plates combined together, or of a single plate. Themagnet I) ismounted upon the base a, and secured thereto by a clamp, e.The soft-iron cores iand t", enveloped in the helices or coils j j, aremounted upon the poles of the permanent magnet b in such a manner as toreceive magnetism therefrom by induction, in: a manner well understood.

The elastic diaphragm m is composed of a thin sheet of metal,card-board, animal tissue, or other suitable material, preferablycircular in form. The edges of this diaphragm are rigidly secured, bymeans of screws or otherwise, to a solid support or frame, It, in thecenter of which is an opening, I, which may be covered with a mouthpiece, k, having an aperture an inch or two in diameter inthe center.

A small electro-magnet, m, is firmly secured, by any convenient means,to the center of the diaphragm m, with its poles facing those of thecores '5 i, and in close proximity thereto, so that it virtually acts asan armature to the cores c t" and the permanent magnet 11. The electriccircuit traversing the apparatus goes from the binding-screw p by thewire 1 to the helices j j; thence, by the wire 2, to the helices of theelectro-magnet on, and from thence, by the wire 3, to the otherbinding-post,p. These helices are so connected that a current passingthrough them will always tend to develop magnetism of unlike polarity inthe ends ofthe cores of the respective electro-magnets which areopposite or facing each other, and consequently they will tend toattract each other with greater or less force, according to the strengthof the existing current.

The operation of my improved apparatus is as follows: Two or moreinstruments being connected together in a telegraphic circuit in amanner well understood, a person desiring to transmit an oralcommunication places his mouth at the aperture of the mouth-piece k ofone of the instrlnnents and speaks into it. The diaphragm m, being fixedat the edges,

7 is thrown into vibrations which correspond in their amplitude and intheir varying intervals with the sound vibrations produced in theatmosphere by the voice of the person speaking into the mouth-piece. Theelectromagnet m, being mounted upon the center of the elastic'diaphragm,partakes of its motion, and its poles are thereby caused to alternatelyapproach and withdraw from the extremities of the permanently-magneticcores z i". The changes in the normal magnetic condition of the softiron of the electro-magnet m and of the cores i i, which are produced bythe vibratory movements of the diaphragm m, induce magneto-electriccurrents in the surroun ding'helices, by the action of a well-known law.The waves or undulations of the electric current produced in this mannernecessarily represent, in every essential particular, the origi nalvibrations of the diaphragm m. At the receiving-station these waves orundulations give rise to varying magnetic intensities in the soft-ironcores 13 i and in the electro-magnet m, which, by their.correspondingly-varyin g mutual attraction, cause the diaphragm m to bethrown into similar vibrations, which are communicated to theatmosphere, and thence to the ear of the listener.

In the arrangement described in my former V 7 application it isnecessary toconstruct thediaphragm either of iron or steel, and ofsufficient thickness to give it the necessary amount of inductivecapacity, and these limitations in respect to material andthickness areunfavorable to the production of the best results. By constructing theapparatus in the manner hereinbefore set forth, this objection isavoided, as the diaphragm may be made of such material and dimensions asare found by experiment toproduce the best acoustic effects. Anotherimportant advantage gained by this mode of construction consists in theincreased rapidity of action which results from employing anelectro-magnet to serve as the armature of the permanent magnet, insteadof a permanently-magnetic or neutral plate of iron or steel, which modeof construction has been found to produce much better results inpractice than the one last mentioned. In order to remove the weight andinertia of the helices of the electro-magnet m from the vibratingdiaphragm, it will often be found preferable to attach the said helicespermanently to the frame of the instrument, and make the soft-iron coremovable within them, the core itself being attached to and supported bythe diaphragm, as before.

I have discovered that the actionof the apparatus is very much improvedby the interposition of thin plates d d of india-rubber or otherequivalent elastic substance between the poles of the stationarymagnetic cores '5 '5 and the armature which is attached to and vibrateswith the diaphragm. These plates of rubber form what are technicallytermed dampers, and bytheir action serve to destroy the minorsympatheticvibrations, which tend to interfere to some extent with the clearness ofthe articulation. The best results are produced when the pressure of themovable ar-.

mature against the dampers is slight. This pressure may be convenientlyregulated by the ordinary devices which are employed to adjust thedistance between the magnet and its armature in all telegraphicinstruments. I have shown'in Fig. 1 a very simple and convenient alarmfor telephonic instruments,

which consists of a cord, 8, attached to the center of the diaphragm,and having its surface prepared with resin or other equivalent material.By passing the thumb and fingers over this cord with a rubbing motion,when in a state of moderate tension, it may be thrown into powerfulvibrations, which. are communicated to the diaphragmm, and thencetelephonically to the diaphragm at the receiving-station, producingtherefrom a sound which may be readily distinguished at some distancefrom the instrument, and serves as a very efficient alarm.

I claim as my invention- 1. One or more helices or coils forming aportion of the main circuit, and. surrounding a core or cores maintainedin a permanentlymagnetic state, in combination with an electro-magnetwhose helices are included in the same circuit, and which is so arrangedas to act as an armature to the first-mentioned core or cores, and anelastic plate or diaphragm capable of responding either to sonorousvibrations traversing the atmosphere or other medium, or tocorresponding electro-magnetic vibrations induced in the cores orarmature by the influence of a current of varying strength traversingthe said helices.

2. An armature attached to or forming a part of an elastic diaphragm, incombination with a damper or dampers interposed between the saidarmature and the stationary core or cores, in the manner and for thepurpose specified.

3. The alarm attachment for telephonic instruments herein described,consisting of a cord having a suitably-prepared surface, attached to theelastic diaphragm, in the manner and for the purpose specified.

In witness whereof I have hereunto set my hand this 28th day ofNovember, A. D. 1877.

AMOS EMERSON DOLBEAR.

